Scanning probe microscopes (SPMs), such as atomic force microscopes (AFMs), are widely used for observing fine irregularities of a sample surface and measuring surface roughness. One observation technique for such scanning probe microscopes, which is known as dynamic mode, involves scanning a cantilever comprising a probe on its free end along the sample surface while causing it to vibrate near its mechanical resonance frequency in the direction toward/away from the sample surface (for example, see patent document 1). For observations using dynamic mode, prior to the observation, it is necessary to measure the resonance frequency of the cantilever to be used and adjust the amplitude and frequency of the signal supplied to the actuator (piezoelectric element) which imparts vibration to the cantilever.
Conventional techniques for measuring the resonance frequency of a cantilever include the method of supplying a fixed amplitude sine wave or square wave signal to the cantilever excitation actuator, varying the frequency, and measuring the amplitude of the cantilever at each frequency. In this case, the measured results are graphically displayed on a display device as an amplitude value (vertical axis) for each frequency (horizontal axis), as illustrated in FIG. 4, the user recognizes the frequency for which the greatest amplitude value was obtained as the resonance frequency based on the graph, and sets that frequency as the cantilever excitation frequency during observation.